Brake structure for wheel rotating device

ABSTRACT

A brake structure for a wheel rotating device includes a motor provided in a wheel and is driven for rotating the wheel, and a braking mechanism for actuating brake to brake the wheel. The motor includes: a motor housing; a stator positioned in and fixed to the motor housing; and a rotor positioned in the motor housing and facing to the stator. The braking mechanism includes: a brake rotor to rotate with the wheel; frictional members to be in contact with the brake rotor for generation of braking force; a pressing force generating unit for generating pressing force of the frictional members so that the frictional members are urged to and pressed against the brake rotor by supplying brake fluid through a brake fluid passage to transmit fluid pressure; and a housing for the pressing force generating unit. The brake fluid passage is formed inside a wall of the motor housing, and is connected to a brake fluid supply port provided in the housing for the pressing force generating unit.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No.11/896,081, filed on Aug. 29, 2007now U.S. Pat. No. 7,938,211, and forwhich priority is claimed under 35 U.S.C. §120, which claims the foreignpriority benefit under Title 35, United States Code, §119(a)-(d) ofJapanese Patent Application No. 2006-231500 filed on Aug. 29, 2006 inthe Japan Patent Office. The disclosure of all of the above-identifiedapplications are herein incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a wheel rotating device for rotating awheel of an automobile, and more particularly to a brake structure for awheel rotating device which can reduce the size of the structure.

In-wheel motor for driving a wheel of an automobile is arranged in alimited space of the wheel. In recent years, attempts have been made todesign layout of various parts so that the size of the whole device canbe reduced while increasing the diameter of the motor for improvingmotor torque. For example, Japanese Laid-open Patent Application No.2004-114858 discloses such a layout design. As a brake structure for thewheel rotating device, hydraulic brake is generally used so that a largebraking force is obtained.

Japanese Laid-open Patent Application No. 2004-114858 discloses anin-wheel motor equipped with a hydraulic braking mechanism. According tothis arrangement, an externally attached hydraulic pressure tubeconsisting of a brake hose is connected between a hydraulic pressuresupply source to be fixed to the vehicle body and a braking device of awheel. This brake hose is arranged so as to extend along the peripheryof a motor housing.

However, since the brake hose extends along the motor housing and isattached externally, it is necessary to ensure mounting space forexternally attached parts at the outer peripheral side of the motor.This makes it difficult to increase the diameter of the motor, and as aresult, torque of the motor cannot be increased. Further, it isdifficult to layout the brake hose.

In view of the above, the present invention seeks to provide a brakestructure for a wheel rotating device which can eliminate the drawbacksas above, and which can reduce the size of the braking mechanismincluding a fluid passage (i.e., brake fluid passage) for brakeapplication.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a brake structurefor a wheel rotating device, which comprises a motor provided in a wheeland is driven for rotating the wheel, and a braking mechanism foractuating brake to brake the wheel. The motor comprises a motor housing,a stator positioned in and fixed to the motor housing, and a rotorpositioned in the motor housing and facing to the stator. The brakingmechanism comprises a brake rotor to rotate with the wheel, frictionalmembers to be in contact with the brake rotor for generation of brakingforce, a pressing force generating unit for generating pressing force ofthe frictional members so that the frictional members are urged to andpressed against the brake rotor by supplying brake fluid through a brakefluid passage to transmit fluid pressure, and a housing for the pressingforce generating unit. The brake fluid passage is formed inside a wallof the motor housing, and is connected to a brake fluid supply portprovided in the housing for the pressing force generating unit.

With this configuration of the brake structure, brake fluid is suppliedfrom the brake fluid passage via the brake fluid supply port and intothe housing, to thereby generate pressing force at the pressing forcegenerating unit. This makes it possible to press the frictional membersagainst the brake rotor to brake the wheel.

Since the brake fluid passage is formed inside the wall of the motorhousing so that an externally attached hydraulic pressure tube such as aconventional brake hose is not required, there is no need to ensurespace for mounting the externally attached parts, which results in apossibility that the diameter of the motor can be increased. Further, itis not necessary to consider the layout of the brake hose, and thenumber of constituent parts can be decreased.

In the aforementioned brake structure, the brake rotor is a disk rotor,and the frictional members are a first frictional member and a secondfrictional member positioned opposite to each other with the disk rotorinterposed therebetween. Further, the first frictional member is fixedto the motor housing and the second frictional member is fixed to thepressing force generating unit, and the pressing force generating unitis accommodated in the housing and is movable in a direction of arotation axis of the disk rotor. Furthermore, the housing is attached tothe motor housing such as to be non-contacting with the outer peripheryof the disk rotor.

With this configuration of the brake structure, the first frictionalmember is fixed to the motor housing. Therefore, it is not necessary toprovide a dedicated mounting member on the housing, which can reduce thesize of the braking mechanism in the direction of the rotation axis ofthe disk rotor. Namely, if the first frictional member is provided in ahousing as with the conventional brake structure, the housing to whichthe first frictional member has been fixed is further attached to themotor housing, thereby increasing the thickness of the brake structure.On the contrary, the above brake structure is configured such that onlythe second frictional member is attached to the housing. This makes itpossible to reduce the size of the brake structure in the axialdirection. Further, a caliper half that is a half member of theconventional caliper can be used for the housing, thereby reducing thecost.

In the aforementioned brake structure, the brake fluid passage may be alinear passage formed inside the wall of the motor housing.

With this configuration of the brake structure, since the brake fluidpassage is a linear passage, it is possible to form the brake fluidpassage in a simple manner, thereby reducing the cost.

The aforementioned brake structure may further comprise a fixing memberfor fixing one of the frictional members. In the brake structure, thebrake rotor is a disk rotor, and the frictional members are a firstfrictional member and a second frictional member positioned opposite toeach other sandwiching the disk rotor therebetween. The first frictionalmember is fixed to the pressing force generating unit, the pressingforce generating unit is accommodated in the housing and is movable in adirection of a rotation axis of the disk rotor, and the housing isformed integrally with the motor housing. Further, the second frictionalmember is fixed to the fixing member, and the fixing member is attachedto the motor housing such as to be non-contacting with the outerperiphery of the disk rotor.

With this configuration of the brake structure, since the pressing forcegenerating unit is accommodated in the housing which is formedintegrally with the motor housing having a sufficient strength, themotor housing can directly receive a reaction force of the pressingforce generating unit. It is also possible to provide a bracket (fixingmember) for fixing the frictional member that is positioned in theopposite side of the pressing force generation side in a simplestructure. Further, the disk rotor can be formed in a flat and simpleform, thereby reducing the cost.

In the aforementioned brake structure, the disk rotor may be a floatingdisk which is movable in a direction of a rotation axis of the diskrotor.

With this configuration of the brake structure, since the disk rotor isa floating disk which is movable in the rotation axis direction of thedisk rotor, it is possible to apply a braking force equally on theopposite frictional member as well as to reduce dragging of thefrictional members against the disk rotor while the brake is not beingapplied. Further, movement of the disk rotor in the axial directionallows the frictional surfaces of the disk rotor to be ensured withoutdeformation of the disk rotor, thereby reducing a deviation of friction.

The aforementioned brake structure may further comprise a wheel rotatingmember for transmitting motor toque to the wheel, and a resilient memberprovided between the wheel rotating member and the floating disk andurging the floating disk in a direction away from the wheel rotatingmember so as to prevent the wheel rotating member and the floating diskfrom being proximate to each other.

With this configuration of the brake structure, the resilient memberfunctions such as to urge the floating disk away from the wheel rotatingmember if the distance between the wheel rotating member and thefloating disk is too narrow. This makes it possible to preventinterference between the floating disk and other parts such as the motorhousing even if the frictional member is worn out and the thicknessthereof becomes thinner. The wheel rotation unit includes, for example,an axle shaft and a hub.

In the aforementioned brake structure, the brake rotor may be a drumrotor. Further, the frictional members are a pair of frictional members,and each of the frictional members has one end which is pivotallysupported and the other end which is attached to the pressing forcegenerating unit. The pressing force generating unit is accommodated inthe housing such as to reciprocate the frictional members in a directionslidably contacting with the inner periphery of the drum rotor, and thehousing is attached to the motor housing.

With this configuration of the brake structure, there is provided a drumrotor type brake with a self-servo characteristic which causes lessdragging and ensures extended area of the pads, and the housing isdirectly attached to the motor housing. This makes it possible to reducethe size of the brake structure in the direction of the rotation axis ofthe drum rotor.

According to the present invention, it is possible to reduce the size ofthe braking mechanism including the fluid passage (i.e., brake fluidpassage) for brake application. Therefore, the diameter of the motor canbe extended to increase the motor torque.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and aspects of the present invention will become moreapparent by describing in detail illustrative, non-limiting embodimentsthereof with reference to the accompanying drawings, in which:

FIG. 1 is an exploded perspective view illustrating the internalstructure of a wheel of an in-wheel motor vehicle according to a firstembodiment;

FIG. 2 is a vertical section showing the overall configuration of abrake structure for the wheel rotating device according to the firstembodiment as viewed from the rear side of the vehicle body;

FIG. 3 is an exploded perspective view of the motor;

FIG. 4 is an enlarged section showing main parts of the reduction gears;

FIG. 5 is am exploded perspective view of the reduction gears;

FIG. 6 is a side view illustrating operation of the reduction gears;

FIG. 7 is an enlarged section showing main parts of the brakingmechanism;

FIG. 8 is an enlarged section showing main parts of the brakingmechanism when the pads are worn out;

FIG. 9 is an exploded perspective view showing the disk rotor and theaxle shaft;

FIG. 10A is an exploded perspective view showing the disk rotor and aspring plate;

FIG. 10B is a plan view illustrating an engagement between the diskrotor and the axle shaft via the spring plate;

FIG. 11 is a vertical section showing the overall configuration of abrake structure for the wheel rotating device according a modifiedembodiment as viewed from the rear side of the vehicle body;

FIG. 12 is an exploded perspective view illustrating the inner structureof a wheel of an in-wheel motor vehicle according to a secondembodiment;

FIG. 13 is a vertical section showing the overall configuration of abrake structure for the wheel rotating device according to the secondembodiment as viewed from the rear side of the vehicle body;

FIG. 14 is an enlarged section showing main parts of the brakingmechanism; and

FIG. 15 is a side view illustrating operation of the braking mechanismaccording to the second embodiment as viewed from the exterior of thevehicle body.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the present invention will be described withreference to the accompanying drawings. Like reference charactersdesignate corresponding parts in the drawings, and detailed descriptionthereof will be omitted.

First Embodiment

A brake structure for a wheel rotating device according to a firstembodiment will be described below. In this preferred embodiment,explanation will be given on the case in which a brake structureaccording to the present invention is adapted to a disk brake. The brakestructure for the wheel rotating device can be adapted to any of thewheels including front right, front left, rear right, and rear leftwheels. In this preferred embodiment, the brake structure will beexplained as an example where it is adapted to the front left wheel.

As shown in FIG. 1, the brake structure for the wheel rotating device(hereinafter referred to as the brake structure B1) is provided insidethe wheel W and equipped with a motor (in-wheel motor) 1 for generatinga rotation force for rotating the wheel W, reduction gears 2 (see FIG.2) for increasing the motor torque while reducing the rotation speed ofthe motor 1 and then transmitting the rotation force to the wheel W, anda braking mechanism 3 for braking the wheel W.

In FIG. 2, the right side is directed to the interior of the vehiclebody, and the left side is directed to the exterior of the vehicle body.In the following descriptions, directions such as right and left aredefined on the basis of the state as shown in FIG. 2.

Configuration of Wheel and Vehicle Body Side

As seen in FIG. 2, a tire T is mounted on the rim of the wheel W, and anaxle shaft 40 as the rotation axis of the wheel W is joined by bolts 43and nuts 44 (see FIG. 1). Meanwhile, a hub holder HS as a bearing memberis joined to a knuckle K that is fixed to the vehicle body. The axleshaft 40 is rotatably inserted into the hub holder HS via bearings B40,B40, so that the rotation force generated by the motor 1 is transmittedvia the reduction gears 2 and the axle shaft 40 and into the wheel W.

The knuckle K has a substantially disk-shaped configuration. The knuckleK is provided with a joint portion Ka at an upper right surface forconnecting the suspension and with a fixing portion Kb at a lower rightsurface for fixing the lower arm. Provided at the center portion of theknuckle K is a center hole Kc for fitting therein the hub holder HS. SeeFIG. 3. The motor housing 11 for the motor 1 is attached to the knuckleK.

Configuration of Motor

With reference to FIGS. 2 and 3, the motor 1 includes a motor housing11, a stator 12 fixed to the inner peripheral surface of the motorhousing 11, and a rotor 13 provided diametrically inside the stator 12so as to face the stator 12.

The motor housing 11 is made of a material which is light-weighed andwith high rigidity, such as aluminum-magnesium alloy. The motor housing11 includes an outer peripheral wall 111 (wall portion) and a bottomwall (wall portion) 112, and an opening 113 is provided at the center ofthe bottom wall 112. The end portion of the outer peripheral wall 111 isfixed to the left side of the knuckle K so that a space is formedbetween the knuckle K and the motor housing 11 for positioning thestator 12, the rotor 13, and the reduction gears 2.

Each of the outer peripheral wall 111 and the bottom wall 112 has apredetermined thickness, and a brake fluid passage 111 a for brake fluidis formed inside the upper part of the outer peripheral wall 111extending along the right and left direction. The brake fluid passage111 a is a linear passage extending through the outer peripheral wall111. As seen in FIG. 2, the right end of the brake fluid passage 111 ais connected via a joint J to a fluid pressure generating means such asa master cylinder (not shown) that is provided in the vehicle body,whereas the left end of the brake fluid passage 111 a is connected to abrake fluid supply port 31 a of the braking mechanism 3 to be describedlater. Since the brake fluid passage 111 a is a linear passage,machining is readily performed to form the brake fluid passage 111 a.

As shown in FIGS. 2 and 3, a mount recess 112 a is formed in the outersurface of the bottom wall 112. As described later, an inner pad 34 isfitted into the mount recess 112 a. See FIG. 1. Further, an inner gearmember 27 having inner gears 27 a is provided along the inner peripheralsurface of the opening 113 formed in the bottom wall 112. The inner gearmember 27 is a part of the reduction gears 2 to be described later, andsecondary gears 26 (see FIGS. 4 and 5) which form a part of thereduction gears 2 are meshed with the inner gear member 27.

The stator 12 is an annular member that is fixed to the motor housing 11along the inner peripheral surface of the motor housing 11. The stator12 is configured such that coils (not shown) are wound around the core.

The rotor 13 is arranged inside the stator 12 with a predetermined spaceso that the rotor 13 and the stator 12 are faced to each other. Therotor 13 is made of a permanent magnet. The rotor 13 rotates when thestator coil of the stator 12 is electrified. The rotation force of therotor 13 is transmitted to the reduction gears 2.

Configuration of Reduction Gears

As seen in FIGS. 4 and 5, the reduction gears 2 consists of a sun gear21 that is fixed to the rotor 13, and a planetary gear assembly 22 thatis rotatably mounted to the sun gear 21.

As shown in FIGS. 4 and 5, the sun gear 21 includes a cylindricalportion 21 b with a flange portion 21 a. The flange portion 21 a isfixed to the rotor 13, and the cylindrical portion 21 b is fitted ontothe hub holder HS via the bearings B20. Since the sun gear 21 is fixedto the rotor 13, the sun gear 21 rotates with the rotor 13 in a unifiedmanner around the hub holder HS. The cylindrical portion 21 b isprovided with external gears 21 c at positions near the left end of thecylindrical portion 21 b. As described later, first gears 25 of theplanetary gear assembly 22 are meshed with the external gears 21 c, sothat the rotation of the sun gear 21 allows the planetary gear assembly22 to be rotatable.

As shown in FIG. 5, the planetary gear assembly 22 includes a casing 23,six gear shafts 24 rotatably supported in the casing 23, plural sets offirst gears 25 and second gears 26 respectively fixed to the gear shafts24, and the inner gear member 27 provided in the motor housing 11.

The casing 23 consists of an inner casing 231 having an annular shape,and an outer casing 232 integrated with the inner casing 231 via aspacer portion 232 a. The casing 23 is fixed to the axle shaft 40 bybolts 28 that extend through the inner casing 231 and the outer casing232. See the lower part of FIG. 4. The casing 23 supports the gearshafts 24 in a direction parallel to the axis of the axle shaft 40 withgears of the first and second gears 25, 26 partly exposed.

Each gear shaft 24 is attached to the casing 23 with both ends thereofrotatably supported by the bearings B21, B22. The first gear 25 and thesecond gear 26 are fixed to the gear shaft 24 along the axial directionof the gear shaft 24. The first gear 25 is meshed with the externalgears 21 c of the sun gear 21 at the inner peripheral side of the casing23. The second gear 26 is meshed with the inner gears 27 a of the innergear member 27 at the outer peripheral side of the casing 23.

As seen in FIG. 6, according to the reduction gears 2 as constructedabove, when the sun gear 21 rotates by the rotation of the rotor 13, theexternal gears 21 c of the sun gear 21 and the first gears 25 fixed tothe corresponding gear shafts 24 are meshed and rotate the gear shafts24. In other words, each first gear 25 functions to rotate the gearshaft 24 to which the first gear 25 is fixed, by the rotation of the sungear 21. Accordingly, when the gear shafts 24 rotate, the second gears26 fixed to the gear shafts 24 and the inner gears 27 a of the innergear member 27 are meshed to rotate the gear shafts 24 along the innerperipheral surface of the inner gear member 27. In other words, eachsecond gear 26 functions to revolve the gear shaft 24 to which thesecond gear 26 is fixed around the axis of the sun gear 21. Therefore,when the sun gear 21 rotates, the casing 23 by which the gear shafts 24are rotatably supported is rotated, and thus the wheel W (see FIG. 2)fixed to the axle shaft 40 that is fixed to the casing 23 can berotated.

The rotation speed of the gear shaft 24 is determined by the ratio ofthe number of gears of the sun gear 21 to that of the first gear 25, andthe revolution speed of the gear shaft 24 is determined by the ratio ofthe number of gears of the second gear 26 to that of the inner gearmember 27. As with the case of this preferred embodiment, it is possibleto increase the reduction gear ratio if the first gear 25 has largernumber of gears than the second gear 26.

Configuration of Braking Mechanism 3

As seen in FIG. 7, the braking mechanism 3 includes a disk rotor 35which rotates with the wheel W through the axle shaft 40, a caliper half(housing) 31 attached to the motor housing 11, a piston 32 (pressingforce generating unit) received in the caliper half 31, and an outer pad33 and an inner pad 34 positioned opposite to each other with the diskrotor 35 interposed therebetween.

The caliper half 31 is attached to an upper left surface of the motorhousing 11. More specifically, the caliper half 31 is attached to themotor housing 11 such as to be non-contacting with the outer peripheryof the disk rotor 35 to be described later, and further has a cylinder31 c at a position facing to the disk rotor 35. The caliper half 31 isprovided at its attachment portion to the motor housing 11 with a brakefluid supply port 31 a, to which a brake fluid passage 111 a isconnected. The brake fluid supply port 31 a communicates with thecylinder 31 c via a brake fluid passage 31 b. Therefore, brake fluid isfed from the brake fluid passage 111 a into the cylinder 31 c. Thecaliper half 31 is a member having a half size of the conventionalcaliper, so that using the conventional parts makes it possible toreduce the cost.

The piston 32 has the shape of a hollow cylinder with a bottom, and isreceived in the cylinder 31 c. Further, a ring-shaped seal member S isprovided between the outer periphery of the piston 32 and the cylinder31. The inner periphery of the seal member S closely contacts with thepiston 32 so as to prevent brake fluid from leaking out from a gapbetween the cylinder 31 c and the piston 32.

The piston 32 reciprocates in the axial direction of the disk rotor 35by the transmission of brake fluid pressure, so that the outer pad 33 isurged to and pressed against the disk rotor 35. During this movement ofthe piston 32, part of the seal member S that is closely in contact withthe piston 32 follows the movement of the piston 32 while deforming. Forthis reason, when the brake fluid pressure is released, the seal memberS returns to the original position by the resilient action of rubber,during which the piston 32 is retuned to the original position by thenegative pressure of the brake fluid pressure and the resilient actionof the rubber. By this configuration, it is possible to maintain thedistance between the disk rotor 35 and the outer pad 33 to a constantvalue.

The outer pad 33 consists of an outer back plate 33 a and an outerfrictional member (frictional member) 33 b. The outer pad 33 is fittedinto the caliper half 31 via a retainer (not shown). When the piston 32moves to urge the outer pad 33 toward the disk rotor 35, the outerfrictional member 33 b is pressed against the disk rotor 35.

The inner pad 34 consists of an inner back plate 34 a and an innerfrictional member (frictional member) 34 b. The inner pad 34 is fittedinto the mount recess 112 a formed in the left surface of the motorhousing 11 via a retainer (not shown).

The disk rotor 35 is a floating disk which rotates with the wheel W in aunified manner and is movable in the direction of the rotation axis ofthe disk rotor 35. The disk rotor 35 moves in the axial direction whenit is pressed by the outer pad 33, and therefore contacts with the innerpad 34. When the outer pad 33 and the inner pad 34 are pressed againstthe disk rotor 35 that is rotating so as to provide a sliding contacttherebetween, frictional force is generated at the contact surfacebetween the slide-contact surface of the disk rotor 35 and the outer pad33 as well as at the contact surface between the slide-contact surfaceof the disk rotor 35 and the inner pad 34, so as to brake the rotationof the disk rotor 35. The disk rotor 35 is attached to the wheel W onlyby interposing spring plates (resilient members) 45 engageable with theaxle shaft 40. Engagement between the disk rotor 35 and the axle shaft40 will be described below.

As shown in FIG. 9, the disk rotor 35 is an annular-shaped flattenedmember having an outer peripheral portion 351 to provide theslide-contact surface and an inner peripheral portion 352 as anengagement portion with the axle shaft 40.

As seen in FIG. 7, the outer peripheral portion 351 and the innerperipheral portion 352 are arranged in the axial direction of the diskrotor 35 via a stepped portion extending therebetween. Further, as shownin FIG. 9, six engagement recesses 352 a are provided at equal spaceintervals along the inner peripheral surface of the inner peripheralportion 352.

The axle shaft 40 includes a shaft portion 41 that is rotatablysupported in the hub holder HS (see FIG. 2) via the bearings B40, B40,and a disk-shaped fastening member 42 that is fixed to the wheel W bybolts 43 and nuts 44 (see FIGS. 1 and 2).

The fastening member 42 has a center portion 421, a flange portion 422extending radially from the center portion 421, and six engagementprojections 423 projecting from the flange portion 422 along theperiphery of the flange portion 422. As shown in FIG. 7, the centerportion 421 has a larger thickness than the inner peripheral portion 352of the disk rotor 35. The disk rotor 35 is movable in the axialdirection by the distance corresponding to the difference between thethicknesses of the center portion 421 and the inner peripheral portion352. The engagement projections 423 are provided at positionscorresponding to the respective engagement recesses 352 a of the diskrotor 35. The spring plate 45 is attached to each engagement projection423 so that each of the engagement projections 423 is engaged with thecorresponding engagement recess 352 a of the disk rotor 35 with thespring plate 45 interposed therebetween.

As shown in FIG. 10A, the spring plate 45 consists of a pair of springplate strips 46, 46, and a joint portion 47 joining these spring platestrips 46, 46.

Each spring plate strip 46 includes a first strip 461 that is joined tothe joint portion 47, and a second strip 462 that is formed by bendingthe first strip 461 at an acute angle as seen from top to provide anL-shaped strip (see FIG. 10B).

The spring plate 45 is configured such that the first strips 461, 461and the joint portion 47 hold the engagement projection 423 of the axleshaft 40 from three different directions, and by stopper strips 461 a,461 a extending from the first strips 461, 461 and by a stopper strip 47a extending from the joint portion 47, the spring plate 45 is engagedwith the engagement projection 423.

As shown in FIG. 10B, each of the second strips 462, 462 is positionedbetween the disk rotor 35 and the axle shaft 40. In the spring platestrip 46, a bent point formed between the first strip 461 and the secondstrip 462 functions as a supporting point 463, whereas a bent pointformed at the distal end portion of the second strip 462 functions as apoint of action 464. The supporting points 463, 463 contact with theflange portion 422 of the axle shaft 40.

As shown by broken lines in FIG. 10B, when the disk rotor 35 displacesinward of the vehicle body along the rotation axis, the second strips462, 462 of the spring plate 45 are pressed by the disk rotor 35 anddeformed toward the axle shaft 40. When the pressing force of the diskrotor 35 is released, the second strips 462, 462 spring back by theresilient action thereof around the supporting points 463, 463 so thatthe disk rotor 35 is pushed back toward the exterior of the vehicle bodyby means of the points of action 464, 464. This can create a push-backstructure for the disk rotor 35, which can prevent interference betweenthe disk rotor 35 and the motor housing 11, even if the inner frictionalmember 34 b of the inner pad 34 is worn out and thickness of the padbecomes thinner as illustrated in FIG. 8 so that the distance betweenthe disk rotor 35 and the motor housing 11 is too narrow (e.g., theposition surrounded by a circle C).

Operation of Brake Structure B1

With reference to FIGS. 7 and 8, the operation of the brake structure B1according to this embodiment will be described. When the vehicle runs,the disk rotor 35 shown in FIG. 7 rotates together with the wheel W. Inorder to brake the vehicle, brake fluid is supplied from a brake fluidpressure generating unit such as a master cylinder (not shown) providedin the vehicle body to the brake structure B1 according to thisembodiment.

Brake fluid is supplied through the brake fluid passage 111 a of themotor housing 11, the brake fluid supply port 31 a of the caliper half31, and the brake fluid passage 31 b and into the cylinder 31 c, therebytransmitting brake fluid pressure to the piston 32. Therefore, thepiston 32 advances toward the inside of the vehicle body to press theouter pad 33 against the disk rotor 35. At the same time, the disk rotor35 is displaced toward the inside of the vehicle body along the axialdirection and pressed against the inner pad 34. As a result, the diskrotor 35 makes sliding contacts between the outer pad 33 and the innerpad 34, so that frictional forces generate between the slide-contactsurfaces of the disk rotor 35 and each of the contact surfaces of theouter pad 33 and the inner pad 34, thereby braking the rotation of thedisk rotor 35.

When the brake fluid pressure is released and the brake structure B1 isin the non-braking state, the piston 32 returns to the original positionby the restoring force of the seal member S so that the gap between theouter pad 33 and the disk rotor 35 becomes large. Meanwhile, the gapbetween the disk rotor 35 and the inner pad 34 is kept because the diskrotor 35 is a floating disk capable of moving in the direction towardthe exterior of the vehicle body when the re-rotating disk rotor 35interferes with the inner pad 34. The disk moves slightly to an extentthat would ensure a gap with respect to the pads, for example, forapproximately 0.1 to 0.2 mm.

As shown in FIG. 8, if the thicknesses of the outer pad 33 and the innerpad 34 becomes thinner during the course of the actual use, the springplate 45 pushes back the disk rotor 35 toward exterior of the vehiclebody so as not to cause interference between the disk rotor 35 and themotor housing 11, for example, at the position surrounded by the circleC.

The brake structure B1 as constructed above has the followingadvantages.

-   (1) Since the brake fluid passage 111 a is formed inside the outer    peripheral wall 111 of the motor housing 11 so that an externally    attached hydraulic pressure tube such as a conventional brake hose    is not required, there is no need to ensure space for mounting the    externally attached parts, which results in a possibility that the    diameter of the motor 1 can be increased to improve the motor    torque.-   (2) Since an externally attached hydraulic pressure tube such as a    conventional brake hose is not required, it is not necessary to    consider the layout of the brake hose, and the number of constituent    parts can be decreased. Further, since the brake fluid passage 111 a    is a linear passage, it is possible to form the brake fluid passage    111 a in a simple manner, thereby reducing the cost.-   (3) Since the inner pad 34 is fixed to the motor housing 11, the    thickness of the caliper half 31 can be reduced accordingly. This    makes it possible to reduce the size of the braking mechanism 3    along the rotation axis of the disk rotor 35.-   (4) Since the disk rotor 35 is a floating disk which is movable in    the rotation axis direction of the disk rotor 35, it is possible to    apply a braking force equally to the opposite outer and inner pads    33, 34 as well as to reduce dragging of the outer and inner pads 33,    34 against the disk rotor 35 while the brake is not being applied.    Further, the movement of the disk rotor 35 in the rotation axis    direction allows the frictional surfaces of the disk rotor 35 to be    ensured without deformation of the disk rotor 35, thereby reducing a    deviation of friction.

Although the brake structure B1 according to one preferred embodiment ofthe present invention has been described in detail, the presentinvention is not limited to this specific embodiment and various changesand modifications may be made without departing from the scope of thepresent invention.

For example, the position of the piston is not limited. As shown in FIG.11, unlike the above embodiment in which the piston 32 is providedoutward of the disk rotor 35 toward the exterior of the vehicle body,the piston may be provided inward of the disk rotor 35 toward theinterior of the vehicle body.

To be more specific, in the brake structure according to this modifiedembodiment, a cylinder 112 a′ for receiving a piston 32′ is provided inthe bottom wall 112′ of the motor housing 11, and a brake fluid passage111 a′ communicating with the cylinder 112 a′ is formed in the bottomwall 112′ and the outer peripheral wall 111. A fixing member 31′ towhich an outer pad 33′ has been attached is further attached to thebottom wall 112′ of the motor housing 11 such as to be non-contactingwith the outer periphery of the disk rotor 35. The disk rotor 35 movestoward the exterior of the vehicle body when it is pressed by the innerpad 34′ that is fixed to the piston 32′ via a retainer (not shown). Thedisk rotor 35 is braked by pressing the inner pad 34′ and the outer pad33 against the disk rotor 35. The disk rotor 35 is attached to the axleshaft 40 via the spring plates 45 from the interior side of the vehiclebody. In other words, according to this modified embodiment, the brakestructure is configured such that the spring plates 45 are attached inthe reverse direction to those disclosed in the first embodiment (seeFIGS. 2 and 11) because the piston 32′ for pressing the disk rotor 35 isprovided in the reverse side (interior side of the vehicle body) to thatof the first embodiment so that the direction in which the spring plates45 push back the disk rotor 35 is also defined in the reverse direction.

Therefore, it is possible to provide the piston 32′ as a pressing forcegenerating unit, the cylinder 112 a′, and the fixing member 31′positioned in the opposite side of the piston 32′ in a simple structure.Further, the disk rotor 35 can be formed in a flat and simple form(flattened plate shape). As a result, the manufacturing cost of theseparts can be reduced.

Although the brake fluid passage 111 a is formed as a linear passage inthe first embodiment, the shape of the brake fluid passage is notlimited to this specific shape. For example, the brake fluid passage maybe formed as a curved passage or bent passage. Also, the brake fluidpassage may include a plurality of straight passages.

Although only one braking mechanism 3 is provided in the firstembodiment, there may be provided another braking mechanism 3 in theopposite position along the circumference of the disk rotor 35. Thisallows the disk rotor 35 to be readily movable parallelly in the axialdirection, thereby reducing a deviation of friction of the disk rotor35.

Further, in the first embodiment, the axle shaft 40 that is rotatablysupported within the hub holder HS is employed as a wheel rotatingmember. However, the wheel rotating member according to the presentinvention is not limited to this specific structure, and it is possibleto employ a spindle shaft onto which a cylindrical hub is rotatablysupported.

Second Embodiment

A brake structure for a wheel rotating device according to a secondembodiment will be described below. In this preferred embodiment, anexplanation will be given on the case in which a brake structureaccording to the present invention is adapted to a drum brake. The brakestructure for the wheel rotating device can be adapted to any of thewheels including front right, front left, rear right, and rear leftwheels. In this preferred embodiment, the brake structure will beexplained as an example where it is adapted to the front left wheel.

As shown in FIG. 12, the brake structure for the wheel rotating device(hereinafter referred to as the brake structure B2) is provided insidethe wheel W, to which a tire T is mounted on the rim. The brakestructure is equipped with a motor (in-wheel motor) 1 for generating arotation force for rotating the wheel W, reduction gears 2 (see FIG. 13)for increasing the motor torque while reducing the rotation speed of themotor 1 and then transmitting the rotation force to the wheel W, and abraking mechanism 5 for braking the wheel W.

In FIG. 13, the right side is directed to the interior of the vehiclebody, and the left side is directed to the exterior of the vehicle body.

As seen in FIG. 13, the brake structure B2 according to the secondembodiment is basically the same as the brake structure B1 according tothe first embodiment as shown in FIG. 2 except for the brake fluidpassage 111 a provided in the motor housing 11 for the motor 1 and thebraking mechanism 3. A description will be given on the motor housing 1for the motor 1 and the braking mechanism 3.

Configuration of Motor Housing 11 for Motor 1

Likewise the first embodiment, the motor housing 11 includes an outerperipheral wall 111 and a bottom wall 112. The motor housing 11 has theshape of a hollow cylinder with a bottom and the right side thereofopens. The motor housing 11 is fixed to the left side of the knuckle Kso that a space is formed between the knuckle K and the motor housing 11for positioning a stator 12, a rotor 12, and reduction gears 2.

Each of the outer peripheral wall 111 and the bottom wall 112 has apredetermined thickness, and a brake fluid passage 111 b for brake fluidis formed inside the upper part of the outer peripheral wall 111extending in the right and left direction. Further, a brake fluidpassage 112 b is formed inside the bottom wall 112 extending in thevertical direction.

The brake fluid passage 111 b is a linear passage extending from theright end portion of the outer peripheral wall 111 and communicatingwith the brake fluid passage 112 b. The brake fluid passage 112 bextends linearly from the intersection point with the brake fluidpassage 111 b to the position where it faces to the wheel cylinder 52 ofthe braking mechanism 5, and the distal end of the brake fluid passage112 b is connected to a brake fluid supply port 52 a of the brakingmechanism 5. Since the brake fluid passages 111 b, 112 b are formed as alinear passage, machining is readily performed to form the brake fluidpassages 111 b, 112 b. The brake fluid passage 112 b is formed bydrilling a passage from the upper end portion of the outer peripheralwall 111 with the passage communicating with the brake fluid passage 111b and thereafter by closing the drill-starting point.

Configuration of Braking Mechanism 5

As seen in FIGS. 14 and 15 and when necessary to FIG. 12, the brakingmechanism 5 includes a drum rotor 51 which is attached between the wheelW and the axle shaft 40, a wheel cylinder 52 fixed to the motor housing11, a pair of pistons 53, 53 (only one piston is shown in FIG. 14)received in the wheel cylinder 52, a pair of brake shoes 54, 54, and aspring 55 interposed between the pair of brake shoes 54, 54.

As shown in FIG. 14, the drum rotor 51 is formed in a flattenedcylindrical shape (see FIG. 12) and is attached between the wheel W andthe axle shaft 40 by bolts 43 and nuts 44. Therefore, the drum rotor 51rotates together with the wheel W.

The wheel cylinder 52 is attached to an upper left surface of the motorhousing 11. The wheel cylinder 52 is provided at its attachment portionto the motor housing 11 with a brake fluid supply port 52 a, whichcommunicates with a cylinder cavity 52 c inside the cylinder via a brakefluid passage 52 b. Therefore, the cylinder cavity 52 c is filled withbrake fluid supplied from the brake fluid passages 111 b, 112 b of themotor housing 11. Reference numeral 52 d of FIGS. 14 and 15 denotes anair vent for discharging air within the wheel cylinder 52 to providefluid tight (oil tight).

As seen in FIG. 15, the pistons 53, 53 are provided in pair in a serialmanner, and each piston 53 is received in the corresponding cylindercavity 52 c of the wheel cylinder 52. The distal end of each piston 53is connected to an output member 53 a, which is further connected to abrake shoe 54.

The piston 53 advances the output member 53 a toward the external sideof the wheel cylinder 52 when brake fluid pressure is transmitted to thepiston 53.

Each brake shoe 54 has a web 54 a in the shape of a semicircular arc, aback plate 54 b fixed to the outer peripheral edge of the web 54 a, anda lining 54 c (frictional member) fixed to the outer peripheral edge ofthe back plate 54 b.

The web 54 a is pivotally supported by an anchor pin P at its lowerportion. The upper part of the web 54 a is connected to the distal endof the corresponding output member 53 a as described above. A spring 55bridges between the pair of webs 54 a, 54 a so that the webs 54 a, 54 aare urged radially inward of the motor housing 11.

The back plate 54 b and the lining 54 c are also formed in the shape ofa semicircular arc corresponding to the web 54 a. In the normal statewhere brake is not applied, the outer peripheral surfaces of the pair oflinings 54 c face to the inner peripheral surface of the drum rotor 51in a non-contacting manner.

Operation of Brake Structure B2

With reference to FIGS. 14 and 15, the operation of the brake structureB2 according to this embodiment will be described. When the vehicleruns, the drum rotor 51 shown in FIG. 14 rotates together with the wheelW. In order to brake the vehicle, brake fluid is supplied from a brakefluid pressure generating unit such as a master cylinder (not shown)provided in the vehicle body to the brake structure B2 according to thisembodiment.

Brake fluid is supplied through the brake fluid passages 111 b, 112 b ofthe motor housing 11, the brake fluid supply port 52 a of the wheelcylinder 52, and the brake fluid passage 52 b and into the cylindercavities 52 c, 52 c, thereby transmitting brake fluid pressure to thepistons 53, 53. Therefore, as shown in FIG. 15, the pistons 53, 53advance the output members 53 a, 53 a toward the external side of thewheel cylinder 52 to thereby extend the upper end portion of each brakeshoe 54 in the outward direction with the anchor pin P functioning as asupporting point. As a result, the outer peripheral surfaces of thelinings 54 c, 54 c are pressed against the inner peripheral surface ofthe drum rotor 51, so that frictional forces generate between theslide-contact surfaces of the drum rotor 51 and the contact surfaces ofthe linings 54 c, 54 c, thereby braking the rotation of the drum rotor51.

When the brake fluid pressure is released and the brake structure B2 isin the non-braking state, the webs 54 a, 54 a returns to the originalpositions by the resilient force of the spring 55 and negative pressureof the brake fluid pressure. Clearance between the drum rotor 51 andeach lining 54 c is properly kept by an automatic clearance adjustingmechanism (not shown) even if the linings 54 c are worn out.

The brake structure B2 as constructed above has the followingadvantages.

-   (1) Since the brake fluid passages 111 b, 112 b are formed inside    the outer peripheral wall 111 and the bottom wall 112 of the motor    housing 11, respectively so that an externally attached hydraulic    pressure tube such as a conventional brake hose is not required,    there is no need to ensure space for mounting the externally    attached parts, which results in a possibility that the diameter of    the motor 1 can be increased to improve the motor torque.-   (2) Since an externally attached hydraulic pressure tube such as a    conventional brake hose is not required, it is not necessary to    consider the layout of the brake hose, and the number of constituent    parts can be decreased. Further, since the brake fluid passages 111    b, 112 b are a linear passage, it is possible to form the brake    fluid passages 111 b, 112 b in a simple manner, thereby reducing the    cost.-   (3) The brake structure B2 employs a drum brake with a self-servo    characteristic and ensuring extended area of the pads, and the wheel    cylinder 52 and the brake shoes 54, 54 are directly attached to the    motor housing 11. This makes it possible to reduce the size of the    braking mechanism 5 in the axial direction than the braking    mechanism 3 with the caliper half 31 according to the first    embodiment.

Although the brake structure B2 according to the second embodiment hasbeen described in detail, the present invention is not limited to thisspecific embodiment and various changes and modifications may be madewithout departing from the scope of the present invention.

Although the brake fluid passages 111 b, 112 b are formed as a linearpassage in the second embodiment, the shape of the brake fluid passageis not limited to this specific shape. For example, the brake fluidpassage may be formed as a curved passage or bent passage.

According to the second embodiment, parts (wheel cylinder 52, brakeshoes 54, 54) of the braking mechanism 5 are directly attached to themotor housing 11. However, the attachment structure is not limited tothis specific embodiment. For example, these parts may be attached tothe motor housing 11 via a back plate so as to facilitate attachment ofthe braking mechanism to the motor housing 11.

What is claimed is:
 1. A wheel, comprising: a motor provided in a wheelfor providing a rotational force to the wheel, the motor having a motorhousing; a brake fluid passage formed in the motor housing; a brake lineextending from the motor housing and in fluid communication with thebrake fluid passage; and a brake applying a braking force to the wheel,the brake comprising: a brake housing; a pair of frictional members; arotor; an actuator moving the friction members from a first disengagedposition to a second engaged position; and a supply port for supplyingbrake fluid to the actuator, the supply port extending through the brakehousing from the brake fluid passage to the actuator, wherein the brakehousing contacts the motor housing so that the supply port is in fluidcommunication with the brake fluid passage.
 2. The wheel of claim 1,further comprising: a connector, the connector having a first endattached to the brake line and a second end attached to the motorhousing.
 3. The wheel of claim 1, wherein the rotor comprises a drum,and wherein each of the frictional members has one end pivotallysupported and the other end which is attached to the actuator, theactuator engaging the frictional members to reciprocate the frictionalmembers against an inner periphery of the drum.
 4. The wheel of claim 3,wherein the actuator includes a cylinder.
 5. The wheel of claim 1,wherein the rotor is a disk, wherein the frictional members are a firstfrictional member and a second frictional member positioned opposite toeach other with the disk rotor interposed therebetween, wherein thefirst frictional member is fixed to the actuator, and wherein theactuator is movable in a direction of a rotation axis of the disk. 6.The wheel of claim 5, wherein the actuator includes a piston.
 7. A brakestructure for a wheel rotating device, which comprises a motor that isprovided in a wheel and driven for rotating the wheel, and a brakingmechanism for actuating a brake to brake the wheel, wherein the motorcomprises: a motor housing that is attached to a knuckle, the motorhousing being in an annular shape and having a center hole; a statorpositioned in and fixed to the motor housing; and a rotor positioned inthe motor housing and facing to the stator, wherein the brakingmechanism comprises: a drum rotor to rotate with the wheel; frictionalmembers to be in contact with the drum rotor for the generation of abraking force; a pressing force generating unit for generating apressing force to have the frictional members urged to and pressedagainst the drum rotor by a fluid pressure transmitted through brakefluid supplied through a brake fluid passage; and a second housing forhousing the pressing force generating unit; wherein the frictionalmembers are a pair of frictional members, and each of the frictionalmembers has one end which is pivotally supported and the other end whichis attached to the pressing force generating unit, wherein the pressingforce generating unit is capable of having each of the frictionalmembers make a reciprocating movement into slidable contact with theinner periphery of the drum rotor, and the second housing contacts themotor housing, and wherein the brake fluid passage is formed inside anouter peripheral wall of the motor housing outside a periphery of theknuckle, and is connected to a brake fluid supply port provided in thesecond housing.
 8. The brake structure according to claim 7, wherein thedrum rotor is disposed in a space between the motor and the wheel andattached to the wheel.
 9. The brake structure according to claim 7,wherein the housing is disposed in a space between the motor and thewheel, and wherein each of the frictional members comprises: a web beingin a shape of a semicircular arc; a back plate fixed on an outerperiphery of the web and a lining fixed on an outer periphery of theback plate; and the web of the each of the frictional members has oneend which is pivotablly supported and disposed in a vicinity of a lowestpoint of the motor housing in a vertical direction.